Utilization of carbonyl-modified carbon nanotubes for selective removal of perfluorinated sulfonates from surface water

The simultaneous treatment addressing large-scale, low-concentration PFAS in natural waters is still a challenge due to the persistence of perfluorosulfonic acid (PFSA) compared to perfluorocarboxylic acid (PFCA). This study presents a breakthrough treatment for PFAS wastewater based on carbonyl multi-walled carbon nanotubes (MWCNTs) for selective PFSA capture. The developed MWCNTs near-completely removed perfluorooctane sulfonate (PFOS) and its substitute 6:2 chlorinated polyfluorinated ether sulfonate (F53-B) from 50 mL of surface water within 5 min from six mixed PFAS solutions with different chain lengths and functional groups, with maximum adsorption capacities of 407.3 mg g −1 and 611.9 mg g −1 , respectively. The material characterization and density functional theory (DFT) calculations revealed that this outstanding performance arises from three synergistic mechanisms: a specific interaction between carbonyl groups and C-F bonds, enhanced electrostatic attraction, and π-π stacking interactions. These interactions enable preferential PFSA even in complex matrices containing humic acid and competing anions. The material maintains excellent stability, with complete F53-B removal sustained over five of adsorption cycles. Notably, the F53-B eluted from MWCNTs was near-completely defluorinated in UV254/sulfite system, effectively mitigating secondary pollution risks. This study provides a new approach to address the key challenges of PFSA and PFCA pollution in natural water, providing reference for the rapid separation of PFSA and the subsequent harmless treatment of residual PFCA, which protect water ecology and water resources security.